Rebuild GeoJSON endpoint

Summary:
- Use Endpoint for posts get, search and delete
- Return total_count for search usecases
- Move GeoJSON formatting to a formatter class and avoid double handling posts
- Remove old code from GeoJSON controller
- Fixup overly specific geojson test

Test Plan:
bin/behat application/tests/features/api.posts.feature
bin/behat application/tests/features/posts/api.geojson.feature

Reviewers: aMoniker, vladimir, shadowhand

Reviewed By: shadowhand

Subscribers: eyedol

Maniphest Tasks: T564

Differential Revision: https://phabricator.ushahidi.com/D537